\centering
\begin{tabular}{cccc}
  \includegraphics[width=60pt]{mini.pdf} & 
  \includegraphics[width=80pt]{mini.pdf} &
  \includegraphics[width=80pt,height=100pt]{mini.pdf} &
  \includegraphics[width=80pt,height=100pt,keepaspectratio]{mini.pdf} \\
  原图 & 放大 & 变形 & 不变形 \\
\end{tabular}
